ASP.NET Object Data Sources

What is an Object Data Source?

In ASP.NET the Object Data Source is a web control that is designed to act as an interface between an object and a data bound control on a web page. This tutorial will show you how to set up an ODS and some of the configuration options that are available when doing so.

The Example

Download Example Project

The application will show conversions between ? and , and will allow the user to enter a start and end temperature to display values between. Firstly we will set up the text input boxes in default.aspx:

<asp:Content ID="BodyContent" runat="server" ContentPlaceHolderID="MainContent">

    <asp:Label ID="startLbl" runat="server" Text="Start Temp (?):"></asp:Label>
    <asp:TextBox ID="startInput" runat="server"></asp:TextBox>
    <br />
    <asp:Label ID="endLbl" runat="server" Text="End Temp (?):"></asp:Label>
    <asp:TextBox ID="endInput" runat="server"></asp:TextBox>
    <br />

</asp:Content>

These need to be set up in order to provide the ODS with parameters it needs. Note, that the parameters can also be acquired from other sources such as the session data, cookies or route data etc.

Next we will write the class to for the object that will be contained in the list returned to the ODS. The class will need to take the ? value as a constructor and convert the value to Fahrenheit when accessed:

public class Temperatures
    {
        int celsius;

        public Temperatures(int C)
        {
            celsius = C;
        }

        public int Celcius
        {
            get
            {
                return celsius;
            }
            set
            {
                celsius = value;
            }
        }

        public int Fahrenheit 
        {
            get
            {
                return convertToF(celsius);
            }
            set
            {
                celsius = convertToC(value);
            }
        }

        private int convertToF(int C)
        {
            return 9 / 5 * (C + 32);
        }

        private int convertToC(int F)
        {
            return 5 / 9 * (F - 32);
        }

    }

Finally we need to write the class for the object that the ODS will “query”. Similar to database query syntax, an ODS can provide SELECT, INSERT, UPDATE and DELETE functions. In order to provide these, we need to write a class with functions for each. The class for this example will provide a method to give us SELECT functionality, so we can fill the table to be displayed on our page:

public class GetTemps
    {
        /// <summary>
        /// Returns a list of Temperatures objects.
        /// </summary>
        /// <param name="start">The start of the temperatures to be displayed in celsius</param>
        /// <param name="end">The end of the temperatures to be displayed in celsius</param>
        /// <returns></returns>
        public List<Temperatures> selectTemps(int start, int end)
        {
            List<Temperatures> list = new List<Temperatures>();

            //loop to add temperatures to list
            for (int i = start; i < end; i++)
            {
                list.Add(new Temperatures(i));
            }

            return list;
        }
    }

That wraps up our coding for the objects.The next step is to set up the ODS and any display controls that it will feed.

Adding the Object Data Source

On the .aspx page that we added the textbox controls to earlier, we will need to add our ODS. They can be dragged into the design or code window from the toolbox and there is also a configuration wizard available from the design view. We want to add the ODS to the page and refer the SELECT method to the GetTemps.SelectTemps() method, and also to use the values from the textbox controls as parameters. The syntax will look something like this:

<asp:ObjectDataSource ID="ObjectDataSource1" runat="server" 
        SelectMethod="SelectTemps" TypeName="WebApplication1.Classes.GetTemps">
        <SelectParameters>
            <asp:ControlParameter ControlID="startInput" DefaultValue="0" Name="start" 
                PropertyName="Text" Type="Int32" />
            <asp:ControlParameter ControlID="endInput" DefaultValue="0" Name="end" 
                PropertyName="Text" Type="Int32" />
        </SelectParameters>
    </asp:ObjectDataSource>

• SelectMethod attribute tells the ODS the name of the method to use for the SELECT functionality.
• TypeName attribute tells the ODS the class for the object. In this case our GetTemps class from earlier.
• The SelectParameters element holds the parameter details for the SELECT functionality.
• The ControlParameter tells the ODS that the parameters are coming from controls on the page, gives the ID of the control, the name of the parameter it will be providing for, and the property that the parameter will come from (in this case the Text property of the textboxes).

From this point the ODS is functional and will provide input for any databound control (for instance gridviews or listviews). If we want show the object data in a table we can use the listview control:

<asp:ListView ID="ListView1" runat="server" DataSourceID="ObjectDataSource1">
        <ItemTemplate>
            <tr style="background-color: #FFFBD6;color: #333333;">
                <td>
                    <asp:Label ID="CelciusLabel" runat="server" Text='<%# Eval("Celcius") %>' />
                </td>
                <td>
                    <asp:Label ID="FahrenheitLabel" runat="server" Text='<%# Eval("Fahrenheit") %>' />
                </td>
            </tr>
        </ItemTemplate>
        <LayoutTemplate>
            <table ID="itemPlaceholderContainer" runat="server" border="1" 
                style="background-color: #FFFFFF;border-collapse: collapse;border-color: #999999;border-style:none;border-width:1px;font-family: Verdana, Arial, Helvetica, sans-serif;">
                <tr runat="server" style="background-color: #FFFBD6;color: #333333;">
                    <th runat="server">
                        Celcius</th>
                    <th runat="server">
                        Fahrenheit</th>
                </tr>
                <tr ID="itemPlaceholder" runat="server">
                </tr>
            </table>
        </LayoutTemplate>
    </asp:ListView>

•  DataSourceID attribute tells the control to databind to the ODS that we created earlier.
• The ItemTemplate element contains the markup to display for each item in the object data source. In this case, we are creating a row in a table for each item, holding a label.
• The text for each label is set using the Eval() method, with the property name as a parameter. It should be noted that that Eval() is only suitable for read only databinding (such as this). If INSERT or EDIT are needed Bind() should be used.
• The LayoutTemplate sets up the markup for the overall layout of the control, in this case a table. The element with the ID attribute of “itemPlaceHolder” marks where the markup for each item will be placed.

The Completed Page

The completed page would produce something along these lines:

Although this page will simply display data generated by inputs from controls on the page, the real power of object data sources comes from allowing the developer to quickly display, edit, insert and delete data from a database or any other object oriented source.

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